1. Field of the Invention
The present invention relates to a cradle bearing that supports a swash plate and the like swingably.
2. Description of the Background Art
Conventionally, a cradle bearing is used as a bearing that supports a swash plate of a swash plate plunger pump as shown in Japanese Unexamined Patent No. 2002-286041. According to the swash plate plunger pump, as shown in FIG. 13, a swash plate 6 is arranged in a circular arcuate recessed part 5a provided in a housing 5 through a cradle bearing 1.
According to this swash plate plunger pump, when the swash plate 6 oscillates, a plunger 7 arranged on a flat surface 6a of the swash plate 6 moves vertically to inhale and feed oil with pressure. In addition, in order to limit the oscillation range of the swash plate 6 within a constant range, the swash plate 6 and the housing 5 are connected through an oscillation amount control member 8.
The cradle bearing 1 used in such swash plate plunger pump comprises a outer race 2 arranged in the circular arcuate recessed part 5a, a plurality of rollers 3 arranged along the inner circumferential surface of the outer race 2 to support the swash plate 6 swingably, and a retainer 4 having pockets for retaining the plurality of rollers 3. In addition, the outer race 2 comprises a positioning projection 2a to engage with a positioning hole 5b of the housing 5 in order to be fixed in the circular arcuate recessed part 5a. 
As shown in FIG. 14, the retainer 4 comprises a pair of circular arcuate members 4a and 4b along the outer race 2, and a plurality of pillar members 4c arranged between the pair of circular arcuate members 4a and 4b. The oscillation amount control member 8 penetrates through the retainer 4 so that the oscillation amount of the retainer 4 is controlled similar to the swash plate 6. In addition, as another means for controlling the oscillation amount of the retainer 4, there is a cradle bearing comprising engagement members provided at both ends of the outer race 2.
In addition, in order to avoid the interference between the pillar member 4c and the swash plate 6, the end face of the pillar member 4c has a contact end face 4d that abuts on the circular arcuate member 4a and a non-contact end face 4e that retreats from the contact end face 4d toward the center side and does not abut on the circular arcuate member 4a. Furthermore, the pocket for housing the roller 3 is formed between the adjacent pillar members 4c. 
The retainer 4 having the above constitution is manufactured by injection molding with a resin material in general, and the stepped part formed between the contact end face 4d and the non-contact end face 4e has a linear configuration as shown in FIG. 15.
Since the outer race 2 having the engagement members at both ends is manufactured by pressing a steel plate in general, the root part of the engagement member 2b that is in contact with a track surface has an R-configuration, that is, a circular arcuate configuration.
Meanwhile, the retainer 4 is manufactured by injection molding with the resin material in general. The corner of the end face of the retainer in the circumferential direction is sharp-pointed because of a problem in cost for processing a conventional injection mold.
Thus, as shown in FIG. 16, the corner of the retainer 4 on the outer side in the diameter direction and the curved root part of the engagement member 2b are linearly in contact with each other, so that stress is concentrated on the contact part. As a result, the retainer 4 could be damaged because it is formed of the resin and has low strength as compared with the engagement member 2b formed of metal.
In addition, according to the cradle bearing 1 having the above constitution, when the swash plate 6 oscillates, the roller 3 rotates around the roller center (refer to as the “rotating motion” hereinafter), and it moves along the track surface of the outer race 2 (referred to as the “revolving motion” hereinafter), and the retainer 4 also moves together with the roller 3.
However, since the range of motion of the retainer 4 is controlled by the engagement members 2b provided at both ends of the outer race 2, when the swash plate 6 oscillates beyond the range of motion of the retainer 4, the pillar member 4c of the retainer 4 hinders the revolving motion of the roller 3. This occurs prominently in a type of bearing that controls the oscillation amount of the retainer 4 by the engagement members provided at both ends of the outer race 2.
At this time, the pillar member 4c receives large load from the roller 3, so that the stress is concentrated on the stepped part 4f, which could cause the retainer 4 to be damaged.